Friday, June 3, 2011

An Old Fashioned Friday Foto Mystery...

The ending of a desert journey leads to a new quest in a land of much water. Let's begin by looking at some rock outcrops that are probably often missed by people whose attention is drawn the opposite direction.

So, the challenge of the day is to name the composition of the rocks, and describe the way that they formed. Extra credit for pointing out where they are, because it will mean you are a traveler of obscure backroads in California.

8 comments:

From here they look suspiciously basaltic. If they are, then I would guess they are pillow basalts, formed as hot lava spilled out onto the ocean floor, interacting with the seawater and the previously formed pillows to cause the unusual shapes. They would have been brought here along with the rest of the package of rocks scraped off onto the accretionary wedge that formed during subduction of the Juan de Fuca Plate.

I admit, though, that I don't know where in California these photos were taken.

I was thinking pillow basalt too, but then remembered that you were in East California; not much there. Then, looking a bit more, it looks like the coast, say Pt. Reyes (cow trails on hills, redwoods in sheltered corner?). So, pillow basalt, Pt. Reyes.

As much as I agree that it resembles pillow basalt, I think that I'd heard once that it was actually weathered sandstone, from along the coast. I've seen such outcrops while driving north of Bodega Bay.

About Me

I am a teacher of geology at Modesto Junior College and former president of the National Association of Geoscience Teachers, Far Western Section. I have led field trips all over the western United States, and a few excursions overseas, but my homebase is the Sierra Nevada, the Great Valley, and the Coast Ranges of California.